1. FIELD OF THE INVENTION
The present invention relates to a flywheel mounting device for an internal combustion engine which is of the type in which the outer peripheral surface of an end portion of a crank shaft of the internal combustion engine is tapered while the inner peripheral surface of a central hole of a flywheel is tapered to form a shape which fits onto the tapered surface of the crank shaft, in which a keyway is formed in the axial direction on each of the tapered surfaces of the crank shaft and flywheel, and in which a key is disposed in the keyway to allow the flywheel to be mounted on the crank shaft. More particularly, the present invention concerns a flywheel mounting device for an internal combustion engine suitable for use in a working machine such as a chain saw.
2. DESCRIPTION OF THE PRIOR ART
In conventional flywheel mounting devices of internal combustion engines of this type, a keyway is formed in the axial direction over the entire length of the tapered inner peripheral surface of the flywheel. As a result, the flywheel is spaced away from the crank shaft at the portion of the keyway at the large diameter end portion of the tapered surface thereof, and the flywheel and the crank shaft therefore do not fit each other along the entire periphery thereof at the large diameter end portions of their tapered surfaces.
In such a flywheel mounting device, since the keyway extends along the tapered surface of the flywheel as far as the large diameter end portion thereof, the coupling portions of the crank shaft and the flywheel may break due to fretting during the rotation of the crank shaft.